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Mass-Matching in Higgsless

Adam Martin, Veronica Sanz

TL;DR

The paper examines mass-matching as a mechanism to suppress the S parameter in 5D Higgsless theories (Cured Higgsless) and analyzes its LHC phenomenology. It shows that tuning light-fermion localization near cL≈1/2 aligns the first KK gauge boson and KK fermion masses, yielding S≈0 while producing measurable collider signatures. Through simulations of single and pair KK-fermion production and KK gauge-boson decays in dilepton and multilepton channels, the work demonstrates that a 700 GeV resonance spectrum could be discovered with less than 10 fb−1 at the LHC, and that observing mass degeneracies across fermionic and bosonic KK towers provides a direct test of the mass-matching mechanism. A large single production of KK fermions would also signal SM quark compositeness, a central feature of the CHL scenario. Overall, the study maps concrete LHC strategies to identify and validate mass-matching as a viability criterion for Higgsless models.

Abstract

Modern extra-dimensional Higgsless scenarios rely on a mass-matching between fermionic and bosonic KK resonances to evade constraints from precision electroweak measurements. After analyzing all of the Tevatron and LEP bounds on these so-called Cured Higgsless scenarios, we study their LHC signatures and explore how to identify the mass-matching mechanism, the key to their viability. We find singly and pair produced fermionic resonances show up as clean signals with 2 or 4 leptons and 2 hard jets, while neutral and charged bosonic resonances are visible in the dilepton and leptonic WZ channels, respectively. A measurement of the resonance masses from these channels shows the matching necessary to achieve $S\simeq 0$. Moreover, a large single production of KK-fermion resonances is a clear indication of compositeness of SM quarks. Discovery reach is below 10 fb$^{-1}$ of luminosity for resonances in the 700 GeV range.

Mass-Matching in Higgsless

TL;DR

The paper examines mass-matching as a mechanism to suppress the S parameter in 5D Higgsless theories (Cured Higgsless) and analyzes its LHC phenomenology. It shows that tuning light-fermion localization near cL≈1/2 aligns the first KK gauge boson and KK fermion masses, yielding S≈0 while producing measurable collider signatures. Through simulations of single and pair KK-fermion production and KK gauge-boson decays in dilepton and multilepton channels, the work demonstrates that a 700 GeV resonance spectrum could be discovered with less than 10 fb−1 at the LHC, and that observing mass degeneracies across fermionic and bosonic KK towers provides a direct test of the mass-matching mechanism. A large single production of KK fermions would also signal SM quark compositeness, a central feature of the CHL scenario. Overall, the study maps concrete LHC strategies to identify and validate mass-matching as a viability criterion for Higgsless models.

Abstract

Modern extra-dimensional Higgsless scenarios rely on a mass-matching between fermionic and bosonic KK resonances to evade constraints from precision electroweak measurements. After analyzing all of the Tevatron and LEP bounds on these so-called Cured Higgsless scenarios, we study their LHC signatures and explore how to identify the mass-matching mechanism, the key to their viability. We find singly and pair produced fermionic resonances show up as clean signals with 2 or 4 leptons and 2 hard jets, while neutral and charged bosonic resonances are visible in the dilepton and leptonic WZ channels, respectively. A measurement of the resonance masses from these channels shows the matching necessary to achieve . Moreover, a large single production of KK-fermion resonances is a clear indication of compositeness of SM quarks. Discovery reach is below 10 fb of luminosity for resonances in the 700 GeV range.

Paper Structure

This paper contains 13 sections, 11 equations, 15 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Higgsless model basics
  3. The Cure: Mass-Matching
  4. Collider Constraints
  5. Identifying the Mass-Matching mechanism
  6. Simulation basics
  7. Single production fermion KK: the $2\,\ell+ 2\ \text{jet}$ channel
  8. Double production fermion KK: the $4\,\ell + 2\ \text{jet}$ channel
  9. Neutral resonances: multiple tiers and nearby states
  10. Charged resonances: $3\,\ell + \hbox{$E$} / _T$
  11. Conclusions
  12. Appendix: Cured Higgsless Parameters
  13. Appendix: Simulation details

Figures (15)

  • Figure 1: Mass matching at work: the mass of the first $Z_{KK}$ state (red) and the mass of the first $Q_{KK}$ as a function of the 5D (left-handed) fermion mass $c_L$. Only values close to $c_L\sim 0.5$ agree with the current value of $S$.
  • Figure 2: $|S|<0.5$ region vs. $c_L$ and $\ell_0$.
  • Figure 3: Masses with $|S|<0.5$ and $|T|<0.3$
  • Figure 4: Couplings with $|S|<0.5$ and $|T|<0.3$
  • Figure 5: Combined $S,T$ constraints (solid line) and the Tevatron bound from high-$p_T$ objects (dotted line)
  • ...and 10 more figures